The invention relates to a throttle valve, and a fluid injection device which is provided with such a throttle valve, for injecting a fluid into a geological formation, and a method for injecting a fluid into a geological formation. The invention further relates to methods for mounting and demounting the throttle valve in an injection tube section.
It is known to store carbon dioxide (CO2) which is produced during natural gas processing or combustion processes in geological formations. Storage of carbon dioxide takes place typically by way of an injection tube which reaches into the geological formation. For reasons of stability, the injection tube is disposed in a bore hole which is encased and cemented as far as the lower region. In order to create a hydraulic communication with the rock formation, the tubes are subsequently perforated in selected regions. From the end region of the injection tube, the CO2 is to be filled over a large space into the pores of the rock of the geological formation.
The injection of CO2 in the liquid state is provided in a technical realization known from practice. With a density of approximately 0.7 kg/dm3 and the required condensation pressure for CO2 during the feeding (approx. 65 bar), at the deepest end of the bore hole (approx. 800 m) the ambient pressure in the geological formation is significantly exceeded by the pressure of the liquid CO2. As a result of the high overpressure, there is a danger of an unwanted change of the rock due to cracks, which can also propagate through the covering layer (e.g. clay or salt) above the storing formation. There is therefore an interest in reducing the pressure of the liquid CO2 in the bore hole by way of a throttle valve.
Numerous types of valves for regulating and interrupting fluid streams are known in all areas of technology. Valves can be differentiated according to the sealing properties, the control properties, the type of drive, the medium flowing through or the application field. By way of example, pinch valves are known from patent documents EP 1 035 360, U.S. Pat. No. 5,535,983 and WO 92/03676, in which the cross-section of a hose-like segment is reduced by an external radial pressure. Although the pinch valves enable a reliable closing function, disadvantages can however result from limited control properties. DE 36 85 640 T2 describes an underground sliding sleeve valve and its installation in a tube. A bore hole valve having a selectively movable valve element is known from EP 0 986 690 B1. DE 69 629 973 discloses a remotely controlled valve having a movable valve stem, which can be activated with the help of liquid. These conventional-valves have disadvantages due to a complex construction and limited functional reliability.
DE 2 549 113 describes a sleeve valve in which the closed state is dependent on the position of a cylindrical sleeve relative to a valve plate. The sleeve is connected to a annular piston, which is mounted in a cylinder with freedom to slide. By applying a pressure medium to the cylinder, the annular piston can be displaced and the sleeve valve actuated in this way. Due to its complex construction and limited ability to accurately adjust the pressure reduction, in particular under high pressure conditions, the sleeve valve according to DE 2 549 113 has significant disadvantages, due to which a use in geotechnical tasks and especially for the injection of CO2, is excluded.
Furthermore, conventional valves generally have at least one of the following disadvantages. Firstly, they do not have both a reliable closing function and a distinctive regulation behavior. Secondly, the energy for the regulation must be supplied by way of separate fluidic or electric lines. Significant limitations with respect to maintenance and exchangeability of the conventional valves represent a further disadvantage.
It is the object of the invention to provide an improved throttle valve, in particular for injecting a fluid into an underground storage, with which the disadvantages of the conventional throttle valves are avoided. It is a further object of the invention to provide an improved fluid injection device with which the disadvantages and limitations of the conventional techniques for injecting fluids into underground storages are avoided. Another object of the invention is to provide an improved method for injecting a fluid into an underground storage, in particular into a geological formation.